It is now well known that an optical disk recorder can provide certain advantages in the data storage arts. Hitherto, the optical disk media utilized for data storage required a relatively tight tolerance of the thickness of the substrate utilized to overcoat the data storage layer. However, any variation in the optical disk overcoat layer thickness causes changes in spherical aberration, away from the design value of the objective lens utilized in the recorder (presently designed to provide acceptably low spherical aberation with a disk having an overcoat substrate of thickness within .+-.20 micrometers of the nominal value); any larger deviation from nominal thickness may result in significant loss of both modulation transfer function (MTF) and spot definition, resulting in unacceptable amplitude loss, so that recovery of data in the reading mode may be rendered impossible. Manufacturers of the optical disk media would like to see even greater tolerances be allowable for the optical disk overcoating layer thickness, as increased tolerance acceptability will have a major negative cost impact. However, even greater substrate thickness tolerances will even more significantly increase spherical aberration. While there is no presently known means for correcting the spherical aberration utilizing the focusing objective lens means of the present optical disk recorders, it is highly desirable to provide some means for correcting spherical aberration, and especially adapted for correction of differing degrees of spherical aberration engendered by the wider range of thicknesses of the optical disk overcoating substrate.